1. Field of the Invention
The present invention relates to a light-emitting device, a method for manufacturing the same, and an electronic apparatus.
2. Description of the Related Art
In recent years, research and development have been actively conducted on light-emitting elements using electroluminescence. In a basic structure of such a light-emitting element, a layer containing a substance with a light-emitting property is interposed between a pair of electrodes. By application of a voltage to this element, light emission can be obtained from a substance with a light-emitting property.
This kind of light-emitting element, which is a self-luminous element, is advantageous in that pixel visibility is high compared to that of a liquid crystal display, that no backlight is needed, and the like and thought to be suitable for use as a flat panel display element. In addition, this kind of light-emitting element is highly advantageous in that it can be fabricated to be thin and lightweight. Furthermore, response speed being extremely fast is one of the characteristics, as well.
Moreover, because such a light-emitting element can be formed into a film shape, by formation of an element with a large area, surface emission can easily be achieved. Because this characteristic is difficult to achieve with point light sources represented by incandescent light bulbs and LEDs or with line light sources represented by fluorescent lamps, the utility value for surface light sources, which can be applied to lighting and the like, is high.
Light-emitting elements using electroluminescence are broadly classified according to whether a substance with a light-emitting property is an organic compound or an inorganic compound.
When a substance with a light-emitting property is an organic compound, electrons and holes are injected into a layer containing an organic compound with a light-emitting property from a pair of electrodes by application of a voltage to a light-emitting element, and then a current flows therethrough. Recombination of electrons and holes (i.e., carriers) places the organic compound with a light-emitting property in an excited state. The organic compound with a light-emitting property returns to a ground state from the excited state, thereby emitting light. Based on this mechanism, such a light-emitting element is called a current excitation type light-emitting element.
The excited state generated by an organic compound can be a singlet excited state or a triplet excited state. Luminescence from the singlet excited state is referred to as fluorescence, and luminescence from the triplet excited state is referred to as phosphorescence.
When such a light-emitting element is used for a display mode such as a display, a partition wall made of an insulator is typically provided between each pixel.
By covering an edge portion of an electrode over a substrate by a partition wall, short circuit between electrodes is prevented. However, if the inclination angle of this partition wall is large, the film thickness of an organic film in a pixel is uneven and peeling occurs between films, which results in a problem called a shrink that is a reduction in light-emitting region of a pixel. A reduction in a light-emitting region greatly decreases the reliability of a light-emitting element.
Further, other causes of short circuit between electrodes include fine particles or the like which remain over the electrode. Because a distance between electrodes of a light-emitting element is usually about 0.1 μm, even a fine particle of about 0.1 μm may easily cause short circuit between electrodes. A light-emitting element in which short circuit occurs between electrodes cannot emit light and is recognized as a dark spot. When a light-emitting element is used as a flat panel display element, such a defect reduces the commercial value of a display panel, which results in an increase in panel cost.
One of methods for preventing short circuit between electrodes which is caused by fine particles or the like is to increase the film thickness of a buffer layer. Unfortunately, however, an increase in film thickness of a buffer layer increases power consumption of a light-emitting element because the conductivity of an organic compound is generally low.